Improving solvent-based self-healing materials through shape memory alloys

Healing of epoxy resins can be accomplished using a combination of embedded ethyl phenylacetate (EPA) solvent loaded capsules and shape memory alloy (SMA) wires. Upon crack formation, the EPA solvent diffuses in the resin and induces swelling which tends to close the crack, while the SMA wires upon heating reduce the crack gap and foster residual epoxy cure. The kinetics of EPA diffusion in the epoxy matrix were measured so as to evaluate the swelling thickness versus time, and concentration at saturation. The largest healable crack gap was found to be 30 μm after 24 h. EPA solvent was shown to lower the curing reaction kinetics and the glass transition temperature (Tg) of the epoxy, as well as its stiffness and strength. Healing efficiency was assessed using long-groove tapered double cantilever beam (TDCB) test samples, with embedded SMA wires across the crack plane. The healing efficiency greatly improved when the crack gap was reduced to 30 μm, from 24% for samples without SMA wires to 78% for samples with SMA wires activated according to an optimized scenario.